Simply put, this is one of the funniest animes I have ever seen. Although I have a weird sense of humor, so Your Mileage May Vary.
Plot: Shinobu, an incredibly incompetent ninja, breaks into Kaede's house to steal her panties so she can pass her master's ninja examination. Kaede and Shinobu become friends, and hang out at the ninja mansion; home to the "master", Onsokumaru (a perverted flying yellow ball voiced by Norio Wakamoto), and a gang of even more incompetent ninja. They are later joined by Shinobu's sister. Hilarity Ensues. Literally. Leans on the fourth wall and parodies everything.
Content: Mostly clean, with the notable exception of Onsokumaru, who is a complete and total pervert, and it shows. There's also some brief nudity and Fan Service shots. (It's mocking Fanservice, of course.)
Almost no tropes that occur are played straight, and those that are, are usually taken to hilarious extremes.
The Christmas episode.
The end credits. Puppet Ninja chasing claymation Onsokumaru around and line dancing to banjo music.
Manages to totally avoid any sort of Cerberus Syndrome, even in the last episode (which parodied it, of course).
The bad:
Only 12 episodes.
This type of absurd humor is really really subject to Your Mileage May Vary. I find it hilarious, but I can understand how others might not like it as much.
Overall: I found this to be absolutely hilarious. It really helps if you're aware of all the conventions and story devices that it parodies. Then again, if you're reading Tv Tropes you probably have some idea. It perfectly avoids the pit that many comedy stories fall into: having a serious, dramatic ending. They point it out, of course; the show mocks itself to the very end and never stoops to taking itself seriously. If you enjoy absurdist humor, you should definitely check this one out.
Seriously not well known enough.
Simply put, this is one of the funniest animes I have ever seen. Although I have a weird sense of humor, so Your Mileage May Vary.